The present invention relates to the rotors of gyrocraft, and it concerns more particularly articulated rotors whose blades are connected to the hub body of the rotor head by means of linking members of the intermediate sleeve type.
The invention relates especially to the rotors of helicopters, of which each blade is linked to the hub of the rotor by linking means comprising advantageously one single articulation for flapping, for drag and for pitch and which are equipped with a device for elastic recall and damping of the blades in drag.
In the best mode of embodiment of the rotor to which the invention relates, the single articulation for flapping, for drag and for pitch which is comprised by the means of articulation of each blade to the rotor of the hub is advantageously an articulation of the type commonly called "laminated spherical stop". This laminated spherical stop comprises an alternating stacking, in the form of a spherical portion, which is arranged between two armatures rigidly linked, one to the hub, and the other to an intermediate sleeve for linking the foot of the blade to the hub. The alternating stacking in the form of a spherical portion is constituted by rigid dishes and by leaves of an elastic material which transmits in compression the centrifugal forces of the blade onto the hub body and allows the angular oscillations of the blade in flapping, in drag and in pitch.
In order to adapt the natural frequency of the blades in drag and to damp the angular oscillations of the blades in drag, the rotor to which the invention relates comprises elements for elastic recall with incorporated damping which are linked between each blade and the hub or between neighboring blades, and which take the form of tie-rods. According to the invention, each assembly for elastic recall with incorporated damping can have an architecture which corresponds to the description below. The assemblies for elastic recall with incorporated damping have the form of a tie-rod, which comprises a central elongated plate, flat and rigid, which is engaged at least partially between two external elongated plates, flat and rigid and in the same direction. The central plate is linked to each of the two external plates by a layer of a visco-elastic material which is PG,4 bonded to the two plates which it links. The central plate has a pivot eye tip at one end which extends on one side, in the direction of the elongated plates, and beyond the external plates; while the external plates have on the other side, a pivot eye tip which extends in the direction of the elongated plates beyond the central plate.